A calculus of challenges and responses

This paper presents a novel approach for concisely abstracting authentication protocols and for subsequently analyzing those abstractions in a sound manner, i.e., deriving authentication guarantees for protocol abstractions suffices for proving these guarantees for the actual protocols. The abstractions are formalized in a process calculus which constitutes a higher-level abstraction of the ρ-spi calculus and is specifically tailored towards reasoning about challenge-response mechanisms within authentication protocols. Furthermore, it allows for expressing protocols without having to include details on the specific structure of exchanged messages. This in particular entails that many authentication protocols share a common abstraction so that a single validation of this abstraction already gives rise to security guarantees for all these protocols. Such an abstract validation can be automatically performed using static analysis techniques based on an effect system proposed in this paper. Finally, extensions to additional protocol classes enjoy a soundness theorem provided that these extensions satisfy certain explicit, easily checkable conditions.